1. Field of the Invention
The invention generally relates to Raman Microscopes and, more specifically, to continuous diode laser stimulated raman gain/loss vibrational microscopes.
2. Description of Prior Art
Raman scattering is used to measure the vibrational spectra in materials. The Raman process is weak. The Raman intensity is −10−6IL about 1 Raman photon is scattered for every 106 laser incident photons. The intensity of Raman signal versus pump laser power is shown in FIG. 1 where spontaneous and stimulated Raman regions are indicated. Enhanced or stimulated Raman Scattering (SRS) can be used for most intensity peaks and narrowest Raman vibration lines. In SRS, the Raman beam from the noise is amplified by the pump beam to get gain. In the teaching here we teach the use of additional seed beam at Raman frequency: one pump photon (Ω) is annihilated (loss) and one strokes photon (Wi) is created (gain). One can achieve large conversion ≥1%. SRS has no background due to electronic χ3 (1, 2) as does CARS—four wave mixing.
In the past SRS gain, one used ps and fs lasers in stimulated Raman setup. Combination of ps or fs lasers, cw Rhodamine dyes and He—Ne lasers were used to enhance vibrational modes.